1. Field of the Invention
This invention relates to a guide rail mounting structure for guiding and supporting, in an information recording and/or reproducing apparatus using a disk-like information recording medium such as an optical disk, a head carriage for effecting the recording and/or reproduction of information on the information recording medium.
2. Related Background Art
In an information recording-reproducing apparatus using an optical disk or the like, a head carriage carrying an optical head thereon is guided and supported by two guide rails and is adapted to be moved radially of the optical disk by driving means such as a linear motor.
Since the positional accuracy of an objective lens provided in the optical head has an influence upon the auto focusing and auto tracking of the optical head and the stability of signal reproduction, highly accurate positioning is required of the head carriage. In order to move this head carriage with good accuracy, the head carriage is designed such that in mounting it on the guide rails, the positioning thereof relative to the bearing of one of the guide rails is effected by fitting and the head carriage is mounted relative to the bearing of the other guide rail by the use of a slot, whereby the mounting dimension error between the guide rails is absorbed. Such an optical head driving device is disclosed in Japanese Laid-Open Patent Application No. 63-184967, etc.
FIG. 1A of the accompanying drawings is a view of the guide rail mounting structure for the prior-art optical head driving device as it is seen from the direction of the optic axis of an objective lens, and FIG. 1B of the accompanying drawings is a view of such structure as it is seen in the direction of arrow A in FIG. 1A which is a direction perpendicular to the optic axis of the objective lens.
In FIGS. 1A and 1B, a motor base portion 2a which is the stator portion of a spindle motor 2 is fixed to a chassis 1 which is the base of the optical head driving device by means of screws 3a and 3b, and a turn table 4 on which an optical disk D which is an information recording medium is placed is mounted on a rotary shaft 2b which is the rotor portion of the spindle motor 2. Two guide rails 5 and 6 are disposed parallel to each other at equidistant positions from the center of rotation of the turn table 4, and one end of each of these guide rails 5 and 6 is positioned by the opposite ends of a positioning member 8 fixed to the chassis 1 by means of screws 7a and 7b, and the other ends of the guide rails 5 and 6 are positioned by the opposite ends of a positioning member 10 fixed to the chassis 1 by means of screws 9a and 9b, and further the opposite ends of the guide rails 5 and 6 are fixed to the chassis 1 and the positioning members 8 and 10 by means of fixing fittings 11-14 and screws 15-18. A head carriage 20 carrying thereon an optical head including an objective lens 19 is supported on the guide rails 5 and 6, and as previously described, a bearing 20a on one side of the head carriage 20 is fitted and mounted on the guide rail 5 and a bearing 20b on the other side of the head carriage forms a slot-like shape and is slidable relative to the guide rail 6 so as to absorb the mounting dimension error between the guide rails 5 and 6. A coil 21 for driving the carriage is mounted on the side edge of the bearing 20a of the head carriage 20, and together with yokes 22-25 and a permanent magnet 26, it constitutes a linear motor 27.
The optical head is a device for converging a laser light from a laser such as a semiconductor laser and applying it to the information recording portion of an optical disk, and converting the reflected light therefrom into an electrical signal and effecting the recording and/or reproduction of information, and the essential portion thereof comprises an optical system and a driving system. The optical system is comprised of elements such as a semiconductor laser, an objective lens (a converging lens), a mirror, a prism and a light receiving diode. The driving system is a mechanism for moving the objective lens (the converging lens), or the optical system including the objective lens, or the mirror or the like following a surface vibration, a track vibration resulting from the rotation of the optical disk (focusing, tracking and the like), and always maintaining the relative positional relation between the optical disk and a converged spot constant, and the chief constituents thereof are a coil, a magnet, a support element and a slide unit. The head carriage 20 may carry the entire optical head thereon, or may assume such a construction that only a part constituting the optical head (the objective lens and the objective lens driving system) is carried on the head carriage 20 and the other part is disposed outside the head carriage 20.
As the optical disk D carried on the turn table 4 is rotated by the drive force of the spindle motor 2, the head carriage 20 is moved along the guide rails 5 and 6 by the drive force of the linear motor 27 and the recording and/or reproduction of information is effected on the optical disk D through the objective lens 19. Here, the positioning members 8 and 10 are used because predetermined mounting accuracy relative to the center of rotation of the spindle motor 2 must be ensured for the guide rails 5 and 6.
The following two are conceivable as the procedure of fixing the spindle motor 2 and the positioning members 8 and 10 to the chassis 1:
(1) To predetermine the fixing positions on the chassis 1, and mount each member thereat.
(2) To fix the spindle motor 2 to the chassis 1, and then newly measure the dimension from the center of rotation and mount the positioning members 8 and 10.
In the case mentioned under item (1) above, highly accurate working becomes necessary for each member and further, the dimensional tolerance of each member cumulates and therefore, highly accurate positioning is difficult, while in the case mentioned under item (2) above, there is the problem that much time is required of the work and mass production is difficult.